Even though Clueless is about high school, Heckerling seems to give each character a profession to emulate in their speech. 

Travis, as Mr. Hall points out, is like a politician giving a victory speech. Cher is obviously negotiating like a lawyer and this influences her careful word choice. 

Notice how there’s not a lot on the page that suggests Travis talks like a skater dude or that Cher’s speech has a twinge of Valley Girl… This kind of thing can be supplied by actors and doesn’t usually need to be super explicit on the page.